1. Field of the Invention
The present invention relates to an active matrix organic electro-luminescence display panel, and more particularly, to an active matrix organic electro-luminescence display panel with a stable image quality.
2. Description of Related Art
Currently, information telecommunication industry has become a mainstream industry, especially for those portable communication display products, which have become a focus of the development. Flat-panel displays are communication interfaces between human and information, thus, the development of the flat-panel displays is especially important. The following techniques are currently applied to the flat-panel display: plasma display panel (PDP), liquid crystal display (LCD), electro-luminescent display, light emitting diode (LED), vacuum fluorescent display, field emission display (FED) and electro-chromic display. Compared with other flat-panel display techniques, the organic electro-luminescence display panel has a tremendous application potential to become a mainstream of the next generation of flat-panel displays due to its advantages of self-luminescence, no viewing-angle dependence, saving power, simple manufacturing process, low cost, low working temperature, high response speed and full-color.
FIG. 1 is a circuit diagram of a conventional driving circuit. Referring to FIG. 1, the conventional driving circuit 100 is suitable for driving an organic electro-luminescence device OEL through a high voltage source VDD and a low voltage source VCC. The conventional driving circuit 100 includes a scan line 110, a data line 120 and a control unit 130. The control unit 130 is electrically coupled with the scan line 110, the data line 120 and the high voltage source VDD, and the organic electro-luminescence device OEL is electrically coupled between the control unit 130 and the low voltage source VCC. Generally, the high voltage source VDD is a positive voltage, and the voltage of the low voltage source VCC is generally 0 volt (in a state of being grounded).
As shown in FIG. 1, the control unit 130 in the driving circuit 100 includes two thin film transistors T1, T2 and a capacitor C. The thin film transistor T1 has a gate G1, a source S1 and a drain D1, wherein the gate G1 is electrically coupled with the scan line 110, and the drain D1 is electrically coupled with data line 120. Moreover, the thin film transistor T2 has a gate G2, a source S2 and a drain D2, wherein the gate G2 is electrically coupled with the source S1, and the drain D2 is electrically coupled with the high voltage source VDD, and the source S2 is electrically coupled with the organic electro-luminescence device OEL. It should be noted that, in the conventional driving circuit 100, the capacitor C is electrically coupled between the gate G2 and the drain D2.
When a scan signal VSCAN is transferred to the scan line 110, the thin film transistor T1 is turned on, and at this time, a voltage signal VDATA transferred from the data line 120 is applied on the gate G2 of the thin film transistor T2 through the thin film transistor T1, and the voltage signal VDATA applied on the gate G2 is used to control the current I passing through the thin film transistor T2 and the organic electro-luminescence device OEL, so as to control the desirable luminance to be displayed by the organic electro-luminescence device OEL. When the voltage signal VDATA transferred from the data line 120 is applied on the gate G2, the voltage signal VDATA also charges the capacitor C, and its reference voltage is the high voltage source VDD. In other words, when the voltage signal VDATA is applied on the gate G2, a cross voltage (|VDATA−VDD|) at both terminals of the gate G2 is recorded by the capacitor C. Ideally, when the thin film transistor T1 is turned off, the capacitor C maintains the voltage (VDATA) applied on the gate G2 of the thin film transistor T2 effectively, but in fact, after a long time operation, the voltage Vs of the source S2 of the thin film transistor T2 always has drifted upwards, so that the voltage difference Vgs between the gate G2 and the source S2 is gradually reduced, and thus causing the luminance to be displayed by the organic electro-luminescence device OEL to be decayed.
In view of the above, the control unit 130 in the driving circuit 100 still cannot stably control the current I passing through the organic electro-luminescence device OEL, and thus, how to make the current I passing through the organic electro-luminescence device OEL be more stable is an important issue in manufacturing an organic electro-luminescence display panel.